Stone sawing strand, or saw wire, is now widely used in quarries and finishing shops for cutting granite, marble, and other types of stone, to prepare it for use for building construction, for monuments, and the like. Normally, such strand will comprise two or three carbon steel wires helically twisted together. The strand is typically 1/8 to 9/32 inch in nominal diameter, with individual wire diameters of 0.064 to 0.144 inch, and it is commonly sold in lengths of as much as 20,000 feet. Conventional practice is to reverse the direction of the helical twist lay at a preselected interval, typically of 25, 50, or 75 feet; the reason for doing so is to maintain a straight kerf as the strand cuts through the stone.
The machine used in connection with such a saw may consist of two or more large diameter sheaves, arranged on parallel horizontal axles generally spaced 20 to 30 feet apart. To provide the saw, the strand is formed into a loop, such as by butt welding or bevel splice brazing the ends, and is mounted about the sheaves in circumferential grooves provided thereon. One of the sheaves is powered, and drives the saw in band saw fashion, typically at a speed of approximately 60 miles per hour.
The stone cutting operation is carried out by placing the stone work beneath the bottom straight section of the saw spanning the sheaves, and simultaneously moving both sheaves downwardly by energizing a downfeed mechanism of the machine, to cause the strand to cut on a vertical plane through the stone. An aqueous slurry of an abrasive material, such as silicon carbide, is continuously pumped to the cutting zone. The interstices of the strand carry the abrasive slurry through and against the cutting plane, to produce the primary cutting action; the slurry also serves to maintain the work and the sawing strand at relatively low temperatures. As a result of such operations, the strand of course wears, and must be periodically changed for maximum efficiency.
Commercially, stone sawing strand is conventionally manufactured from round, hard drawn, high carbon bright steel wire, using a tubular stranding machine. Briefly, in such a machine the wire is pulled from mounted bobbins through and along a revolving tube, to a closing die where the wires converge in helical configuration; the pitch of twisting or helical assembly is called the "lay length", and will generally range from 5/8 to 11/2 inches. Pulling force is provided by a capstan or wheel located downstream of the closing die, and the capstan is mechanically linked to the rotating strander tube so that the ratio of twist per-unit-length of strand pulled can be precisely controlled. From the capstan, the strand is passed through straightener rolls to a wooden reel suitable for handling and shipment.
A tubular stranding machine is typically 30 to 40 inches in diameter, 12 to 18 feet long, and of several thousand pounds mass. Because most sawing strand is produced with reverse lay direction, the stranding machine must constantly accelerate from zero speed to about 300 revolutions per minute, run for a time at that speed, decelerate to zero, reverse direction, and repeat the cycle; a typical cycle is 21/2 to 31/2 minutes, and gross machine output will generally be approximately 1,200 feet per hour. Such repetitive cycling, and reversal of movement of the large masses involved, necessarily involve large inertial forces and create much wasted energy and loss of efficiency. Machinery maintenance costs are also high, as compared to those required in connection with continuous lay stranding machines.
The prior art suggests a considerable variety of stone sawing strand constructions; the following patents, issued in the United States (except in the instance noted), are exemplary:
A three-wire stone cutting saw is taught in Wienholz U.S. Pat. No. 2,123,619, wherein the wire elements may be triangular, diamond shaped, or flat rectangular strips. The wires may be given a secondary twist, with a pitch that is relatively long in comparison to that of the primary twist.
The stone sawing strand disclosed in Dessureau et al U.S. Pat. No. Re. 24,660 is comprised of two wires of half square/half round cross sectional configuration. The patentees indicate that the twist may be reversed at intervals, and that such is a common practice.
Stevens U.S. Pat. No. 2,876,761 discloses a helicoidal saw wire consisting of a metal strip, which has a portion of reduced thickness intermediate its side edges.
A diamond coated wire saw, made from a braid of wires, is disclosed in Barron U.S. Pat. No. 3,150,470.
Horton teaches, in U.S. Pat. No. 3,180,687, a structure for enlarging the kerf in a rock body, utilizing a sizing saw consisting of a plurality of elongated sections of progressively larger cross-sectional dimensions.
A wire sawing strand comprised of substantially elliptical wires, which is made by compressing a pair of twisted round wires, is described in Joy U.S. Pat. No. 3,257,792.
Thakus U.S. Pat. No. 4,015,931 also discloses a wire saw made by mechanically reworking the cross-sectional configuration of the component strands; in FIG. 5, strands originally of square cross-section are shown.
French patent No. 1,160,447 discloses a stone saw, which may evidently be comprised of square wires.
In the Winter, 1980 edition of BARRE LIFE (published by the Barre Granite Association of Barre, Vt.) is found an article describing the use of steel cutting wire to saw quarry blocks into slabs.
Despite the foregoing, a need remains for a stone sawing strand, and saw produced therefrom, which is capable of highly effective and accurate cutting action, and which can be produced in a manner that is easier, faster, and less expensive than has heretofore been possible.
Accordingly, it is a broad object of the present invention to provide a stone sawing strand which is highly effective and accurate in its cutting action, and which can be produced with greater facility, at increased rates, and at substantially lower cost than have heretofore been possible for the manufacture of comparable products.
It is a more specific object of the invention to provide such a strand wherein the component wires can be helically wound together in a continuous, unidirectional lay, thereby obviating any need for reversal of the stranding machine to provide a saw structure capable of producing a straight kerf through the stone.
Additional specific objects of the invention are to provide a novel stone sawing strand which is relatively light in weight and durable, and has high grit-carrying capacity, thereby permitting high-speed operation and increased output, with reduced power consumption and materials utilization.
It is a further object of the invention to provide a novel method for the production of a stone sawing strand having the foregoing features and advantages, which method enables the utilization of a relatively high-speed and lightweight stranding machine for improved productivity and lower power consumption.
Yet another object of the invention is to provide a novel stone cutting saw produced from the strand and by the method of the invention.